The invention relates to a process for depositing layers based on metal oxide(s), and more particularly those which are, at least slightly, electrically conductive. It relates more particularly to the layers which because of their intrinsic properties and their thicknesses are transparent, without, however, excluding opaque layers.
The invention relates especially to the deposition of such layers on transparent substrates, of the glass or polymer-based organic substrate type. Many products based on transparent substrates in fact require such layers, either in the form of a continuous coating, which may be the case for example with a layer having an antistatic function, having a low level of conductivity or having a heating function, or in the form of a discontinuous coating which is etched in a given pattern. This is, for example, the case with substrates which require conducting elements/electrodes with a good or even high resolution: they may be electrodes for the glass substrates of emissive screens of the flat screen type, electrodes for photovoltaic cells or arrays of conductive elements for heated windows, windows provided with an antenna or glazing with a conductive coating having the function of a shield towards electromagnetic waves.
Many deposition techniques have already been studied for this type of layer. Thus, it is known to manufacture layers based on metal oxide or on silicon oxide via the so-called xe2x80x9csol-gelxe2x80x9d process, the principle of which is like the synthesis of organic polymers and consists in forming an oxide network by polymerization of molecular precursors in solution of the metal alkoxide type, by hydrolysis and then gradual condensation at ambient temperature. A heat treatment makes it possible, in the final step, to dry and densify the layer of oxide obtained.
This process is advantageous in the sense that it is quite flexible in terms of use and is quite simple to employ. However, it includes a number of limitations. Thus, it is not always possible to obtain the optimum layer performance characteristics, for a given chemical composition. Furthermore, up until now it has been possible to obtain only continuous layers which must then be etched using an independent process if a discontinuous patterned layer is desired.
The object of the invention is therefore to remedy these drawbacks via providing an improved process for synthesizing layers based on metal oxides(s) by the sol-gel route, which especially makes it possible to obtain higher performance layers and/or layers which are either continuous or discontinuous.
The object of the invention is first of all a process for depositing via the sol-gel route a continuous or discontinuous layer based on metal oxide(s) on a substrate, especially of the transparent type. This process includes at least the following steps:
(a)xe2x80x94preparation of a sol from at least one metal precursor, at least one chelating/stabilizing agent, optionally at least one solvent and/or at least one dopant precursor,
(b)xe2x80x94deposition of the sol as a layer on at least part of one of the faces of the substrate,
(c)xe2x80x94irradiation by ultraviolet rays of at least part of the sol deposited as a layer on the substrate,
(d)xe2x80x94heat treatment of at least that part of the sol which was irradiated by the ultraviolet rays.
The term xe2x80x9cdiscontinuousxe2x80x9d layer is understood to mean, in the sense of the invention, a layer which is obtained directly in a non-continuous form, in a given pattern, like those which are usually obtained by etching starting with a continuous layer.
For the sake of simplicity, in all the steps of the process described above only the formation and the use of a xe2x80x9csolxe2x80x9d will be mentioned, using a terminology as in the field of sol-gel processes. However, it is clear for those skilled in the art that this xe2x80x9csolxe2x80x9d, once deposited as a layer on the substrate, is able to be converted into a gel by modification of its viscosity brought about by the reactions between the various chemical species contained in the sol.